The present invention relates generally to ultraviolet (UV) cured coatings, and more particularly to UV curable coatings which have demonstrated high gloss, improved scratch and abrasion resistance and other properties excellently suited for overlay and other compositions, as well as to processes of their use and to coated articles resulting therefrom.
It is known to the art that conventionally cured coatings have significant disadvantages. In general, the topcoat and the curing agent are applied separately, in a particular sequence and at particular concentration levels. Because both the proportions of the ingredients and the timing of their application is critical, conventionally cured topcoats have been difficult and costly to apply, especially with the efficiency and consistency required in modern commercial applications.
Ultraviolet (UV) cured coatings overcome several disadvantages associated with conventional topcoat finishes. In particular, UV cured topcoats may be premixed so that the polymerization initiator is added to the active ingredients by the manufacturer when the coating is produced, and not by the coating user when the coating is to be applied. Thus, mixing and measurement errors can be avoided and a more consistent product can be obtained.
Despite their many advantages, UV curable coating compositions pose problems which must be addressed. For example, typical UV topcoats are high molecular weight, highly crosslinked films formed from highly reactive acrylate functionality. As such, known UV topcoats have suffered from limited durability, have been prone to cured resin shrinkage, and have required high doses of UV light to cure. UV topcoats formulated to overcome these problems typically suffer from a loss of durability or processibility, including diminished scratch resistance, abrasion resistance, weather resistance, chemical resistance, stain resistance, thermal stability and adhesion.
Also, importantly, known UV topcoats upon curing have long proven to form rigid, unflexible and unyieldable coatings. Thus, problems have been experienced in the industry where topcoat overlaid materials have been subjected to conditions causing expansion or contraction of the product during processing or in the field of use. For example, UV topcoats overlaying dark, e.g. black finishes which expand upon heating have been known to crack, form other imperfections, or even cause bending or warping of the substrate due to tensions built up in the materials.
In light of the foregoing, a need exists for a UV curable composition which is conveniently processible and which forms coatings exhibiting improved physical and chemical properties, e.g., improved flexibility, durability, scratch resistance, abrasion resistance, thermal stability, crack resistance, chemical resistance, stain resistance, weather resistance and adhesion.